"Weber Carburetors" by Pat Braden, published by HP books has lots of carb theory but little on IDF carb on boxter style motors...

I have all three on reference shelf and use them all at various times....

As for carb choices, a lot will depend of application.... If you are staying within 1600-1700 cc displacement range the kadrons are probably more desirable, if you are above 1700 into 2000 cc range 40 IDFs are good, if you are in 1800 - 2200 cc range 44 or 48 IDF are good choices.... Much will depend on engine size and venturi size and jetting options of carbs....

IF you want WEBER IDF style carbs but what to save a few pennies, consider EMPI HPMX carbs they are surpassing the true WEBER for quality and performance... And are so close a copy the parts interchange....

Dale

Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"